Storage batteries have been widely used as a backup power source in many fields, such as industrial manufacturing, transportation, communication, etc. It is necessary to check and maintain storage batteries regularly to avoid problems that might be caused due to failure or insufficient capacity of the storage batteries. As shown in FIG. 1, a conventional battery tester 200 generally includes a main body 201 and a pair of test leads 202 coupleable to the main body 201. When measuring parameters of a battery or a battery pack with such a battery tester, an operator needs to first operate the main body to set suitable testing mode and measuring conditions. After the testing mode and measuring conditions are set, the operator can press a start key, and then hold a test lead in each hand to make the test leads contact with the anode and the cathode of the battery or the battery pack to be tested, respectively. The main body of the battery tester can process the electrical signals from the test leads to obtain testing results, show the results on a display on the main body, and/or store the results in the memory of the main body. Since the main body usually has a relatively large size and weight, it is often put in a fixed place during the testing. If the operator wants to change the testing mode or some testing conditions during the testing, he or she may need to return to and operate the main body, or ask someone else to operate the main body, which may significantly reduce efficiency. In addition, the operator may need to turn around to check the testing results shown on the display of the main body, which is quite inconvenient for the operator.
In order to overcome the shortcomings mentioned above, an enhanced test lead, which includes a display for showing the test information and a button or buttons for controlling some functions of the battery tester, has been made. In such a test lead, the display, the button(s), and the test terminal share the electrical circuit for exchanging information with the main body of the battery tester. Due to the common circuit shared by the display, the button(s), and the testing terminal, the test lead has a large size and complicated circuit. Furthermore, the wire communication between the display/button(s) and the main body is realized by a signal having a frequency close to that of the current flowing through the testing circuit, so the wire communication between the display/button(s) and the main body may interfere with the measurement and thereby reduce its accuracy.